branching strategy for COSA for Openshift

Typically we have branched COSA everytime we branch for a new OCP release. i.e. the rhcos-4.18 branch is for OCP 4.18 builds.

This has served us well, but we are moving in OpenShift to a model where we do a base image build that is purely RHEL content and no OCP content and using that rhel content stream (i.e. rhel-9.6) as the input to a layered container build that adds the OCP content.

This means we'll use a base RHEL stream (like rhel-9.6) for multiple versions of Openshift at the same time. Ultimately the branching of COSA might not make sense anymore since there is no 1:1 relationship between RHCOS stream to Openshift release.

We could either:

1. Stop branching at all and just use latest
2. Maybe branch differently where we branch for the rhel stream verses an openshift release

With the first option we'd have to be more careful about large changes (like big new features) and with the second option we'd probably need to "backport" a lot of changes from one branch to another as we'd have multiple branches that are essentially latest development streams.

WDYT?

Review the current COSA branching convention described in this issue, especially the relationship between rhcos-* branches, RHEL content streams, and OpenShift releases. Compare the proposed latest-only and RHEL-stream branching models, then document a decided strategy and its backporting implications as the outcome.